Protein translation is an essential and highly regulated cellular mechanism leading to the expression of proteins. However, protein synthesis is often miss-regulated in human diseases, such as cancer. Translation initiation occurs normally in a cap-dependent mechanism but in stressed and cancerous cells translation initiation might be mediated via Internal Ribosome Entry Sites (IRES). IRES-mediated translation accounts for the expression of some tumor-promoting factors in stressed and cancerous cells. Auxiliary RNA-binding proteins, referred to as IRES-Trans-Acting Factors (ITAF), support IRES-mediated translation. Thus, targeting specific ITAF:IRES interactions required to stimulate the IRES-mediated translation of tumor-promoting factors represents an innovative therapeutic approach and targets a cellular mechanism often activated in cancerous cells. Our long-term goal is to identify small molecule inhibitors for specific ITAF:IRES interactions, to demonstrate their functionality in repressing selectively the translation of tumor promoting factors and to develop such molecules to novel anti-cancer drugs. To reach this goal the research in the applicant's laboratory focused on the development of high-throughput assays to screen for compounds inhibiting the functionality of the RNA-binding protein La, a well-known ITAF. The applicant recently published that the ITAF La is overexpressed in different types of tumors (e.g. oral, cervical cancer), stimulates cell proliferation and acts as ITAF during IRES-depending translation of tumor-promoting factors, such as the cooperative oncogene cyclin D1. The central hypothesis is that small molecule inhibitors of La-stimulated cyclin D1 IRES-mediated translation will reduce proliferation of cancerous cells. The rationale is that we found that depletion of La in cancerous cells reduce cyclin D1 expression and cell proliferation. Our strong set of preliminary data guided us to develop three Specific Aims to challenge our hypothesis. In Specific Aim 1: we aim to screen for small molecules inhibiting the functionality the RNA-binding protein La. In Specific Aim 2 we anticipated to demonstrate activity and specificity of compounds identified in the primary screen, and finally in Specific Aim 3 we wish to demonstrate the functionality of lead compounds in cell-based assays. The approach is innovative because it uses novel HTS-assays to screen for inhibitors of protein:RNA interactions which playing a critical role in tumorigenesis. The proposed research is significant, because identification of novel molecules inhibiting La:RNA interactions would signify a proof of concept. Furthermore it is anticipated that the proposed research would represents a substantive departure from the status quo and would illuminate the extremely wide and diverse field of protein:RNA interactions as potential drug target. Ultimately, such knowledge might be translated into new therapeutic strategies targeting the expression of tumor-promoting factors in cancer.